death by a thousand cuts: micro-air vehicles (mav) in the service of air force missions

7/29/2019 DEATH BY A THOUSAND CUTS: MICRO-AIR VEHICLES (MAV) IN THE SERVICE OF AIR FORCE MISSIONS

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AU/AWC/___/2001-4

AIR WAR COLLEGE

AIR UNIVERSITY

DEATH BY A THOUSAND CUTS:

MICRO-AIR VEHICLES (MAV) IN THE SERVICE OFAIR FORCE MISSIONS

byArthur F. Huber, II, Lt Col, USAF

A Research Report Submitted to the FacultyIn Partial Fulfillment of the Graduation Requirements

Advisors: Dr. Grant HammondCol Ted Hailes, USAF (Ret.)

Maxwell Air Force Base, Alabama

April 2001

Distribution A: Approved for public release; distribution is unlimited


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Report Documentation Page

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Title and Subtitle

Death by a thousand Cuts: Micro-Air Vehicles (MAV) inthe Service of Air Force Missions

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Huber II, Arthur F.

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Air War College Air University Maxwell AFB, AL

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Approved for public release, distribution unlimited

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The original document contains color images.

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86


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Disclaimer

The views expressed in this academic research paper are those of the author and do

not reflect the official policy or position of the US government or the Department of

Defense. In accordance with Air Force Instruction 51-303, it is not copyrighted, but is

the property of the United States government.

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Contents

Page

DISCLAIMER.................................................................................................................... IIILLUSTRATIONS .............................................................................................................VTABLES ........................................................................................................................... VITHE AUTHOR ................................................................................................................ VIIPREFACE......................................................................................................................... IXABSTRACT...................................................................................................................... XIINTRODUCTION ...............................................................................................................1WHY MICRO-AIR VEHICLES? .......................................................................................4

What Makes Micro-Air Vehicles Unique?....................................................................4What Is the Basis for an Air Force Interest in MAVs? .................................................7Who Else Is Interested in MAVs? ...............................................................................12

Military ..................................................................................................................13

Civilian ..................................................................................................................15THE STATE OF MICRO-AIR VEHICLE TECHNOLOGIES ........................................17

Aerodynamics..............................................................................................................20 Flow Character ......................................................................................................20Flight Controls.......................................................................................................21

Propulsion....................................................................................................................23 Internal-combustion Engines.................................................................................24Pulse Jet Engines ...................................................................................................25Microjets................................................................................................................25 Electric Motors ......................................................................................................27Reciprocating Chemical Muscle............................................................................27

Energy Generation and Storage...................................................................................28Guidance and Navigation ............................................................................................30Communications..........................................................................................................33 MAV Payloads ............................................................................................................34

Imaging Sensors ....................................................................................................35Nuclear, Biological, and Chemical (NBC) Agent Sensors....................................37Targeting, Tagging, and Identify Friend or Foe (IFF)...........................................38

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Explosives and other Lethal Payloads ...................................................................39Electronic Warfare Payloads .................................................................................40Sniffing Sensors.....................................................................................................41Acoustic Sensors....................................................................................................41Other Payloads.......................................................................................................42

MICRO-AIR VEHICLE SUPPORT TO USAF FUNCTIONS ANDLIKELY EMPLOYMENT CONTEXTS ....................................................................44MAV Operational Limitations.....................................................................................45

Range.....................................................................................................................45 Autonomy ..............................................................................................................46Precision ................................................................................................................46Endurance ..............................................................................................................47Damage Potential...................................................................................................47Weather..................................................................................................................47

Aerospace Power Functions Applicable to MAVs......................................................48Offensive Counterair (OCA) .................................................................................48Interdiction.............................................................................................................48 Close Air Support (CAS).......................................................................................48Strategic Attack .....................................................................................................49Offensive Counterinformation (OCI) ....................................................................50Command and Control (C2)...................................................................................50 Special Operations Employment ...........................................................................51Intelligence, Surveillance, and Reconnaissance (ISR) ..........................................52Combat Search and Rescue (CSAR) .....................................................................53Weather Services ...................................................................................................53

MAV Employment Contexts.......................................................................................54Military Operations Other Than War (MOOTW). ................................................54Limited Raids ........................................................................................................58Insurgent Warfare ..................................................................................................60Conventional Warfare............................................................................................62Warfare Involving Weapons of Mass Destruction (WMD) ..................................63

SUMMARY AND CONCLUDING THOUGHTS ...........................................................64GLOSSARY ......................................................................................................................69BIBLIOGRAPHY..............................................................................................................71

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Illustrations

PageFigure 1 Comparison of the Micro Air Vehicle (AV) Flight Regime with Others ..........6

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Tables

Page

Table 1. UAV Classifications, Characteristics, & Examples..............................................5Table 2. Baseline MAV Weight Distribution ...................................................................19

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The Author

Lieutenant Colonel Arthur F. Huber, II, is a flight test engineer whose career has

spanned various assignments within the weapon systems acquisition process. He holds

Bachelor degrees in Aerospace Engineering and Government & International Relations as

well as a Master of Science degree in Aerospace Engineering, all from the University of

Notre Dame. He is a distinguished graduate of the Air Force Reserve Officers Training

Corps and Squadron Officer School. He was an Air Force Fellow at RAND for in-

residence Intermediate Service School and is currently a student at the Air War College.

Lieutenant Colonel Huber started his military career assigned to the Air Force Space

Technology Center as a staff plans officer, space-based surveillance technology program

manager, and executive officer to the commander. While there, he was selected to attend

Air Force Test Pilot School and graduated in June 1990 after completing the flight test

engineer curriculum. He was then assigned to the 46th Test Wing where he rose to the

position of Branch Chief while managing flight test activities for technology

demonstrations, air-to-air missile development, safe separations, and avionics integration.

During his RAND tour, then Major Huber performed policy research on military

acquisition reform, counter-proliferation of weapons of mass destruction, laboratory

quality measurement, and reachback operations. Subsequently, he transferred to the

Pentagon where he performed duties as a Program Element Monitor for electronic

warfare and air-to-air missile programs within the Office of the Assistant Secretary of the

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Air Force for Acquisition. Thereupon, he was selected to command the 413th Flight Test

Squadron during its busiest period ever accruing over 2000 test hours per year in support

of electronic warfare systems development and testing.

Lieutenant Colonel Huber has been assigned as an aircrew member in multiple

aircraft systems accruing approximately 100 hours in utility class planes and another 425

hours in high-performance aircraft to include the F-4, F-15, F-16, and T-38. His military

decorations include the Meritorious Service Medal with three oak leaf clusters, Air Force

Achievement Medal with one oak leaf cluster, and the National Defense Service Medal.

He is a recipient of the 1983 Notre Dame Zahm Award in Aeronautical Engineering, the

Air Force Space Technology Center Company Grade Officer of the Year for 1986, the

1993 Munitions Test Division Supervisor of the Year, the Defense Systems Management

College Acker Award for Communications Excellence, and Association of Old Crows

Integrated Product Team Award for 2000.

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Preface

What are the potential Air Force applications of emerging micro-air vehicle (MAV)

systems and supporting technologies and what are the implications of this potential for

the execution of military operations? These are the central questions which motivated the

development of this research paper. As an Air War College (AWC) student in an elective

class sponsored by the Center for Strategy and Technology (CSAT), I was afforded the

chance to delve into this area, one that I have been watching with interest for several

years. I have found this area to be of personal and professional interest because it harks

back to the aerodynamics research I conducted as a graduate student at the University of

Notre Dame. Also, it opens up possibilities for enhancing the asymmetric advantages of

air power enjoyed by the United States as compared with the rest of the world.

While I am solely responsible for the work represented by this research paper, it

could not have come to fruition without the key contributions of several people. At the

top of the list are my wife, Beth, and daughter, Juliann, who endured many late nights in

which I worked away on this research. I am pleased to acknowledge the sage guidance

and key insights provided by my CSAT advisors, Dr. Grant Hammond and Colonel (Ret.,

USAF) Ted Hailes. Several professionals in the field of micro-air vehicle development

also deserve praise for reviewing this manuscript and they include Dr. William Davis and

Mr. David Johnson of MIT Lincoln Laboratory, Dr. Thomas Mueller of the University of

Notre Dame, and Dr. Steven Walker of the Air Force Office of Scientific Research.

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Lastly, I thank my fellow CSAT and AWC Seminar 3 classmates for their genuineinterest in this research topic and their constructive comments to make it a better product.

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AU/AWC/___/2000-12

Abstract

Technological progress in a number of areas to include aerodynamics, micro-

electronics, sensors, micro-electromechanical systems (MEMS), micro-manufacturing,

and more, is ushering in the possibility for the affordable development and acquisition of

a new class of military systems known as micro-air vehicles (MAV). MAVs are a subset

of uninhabited air vehicles (UAV) that are up two orders of magnitude smaller than the

manned systems that permeate our contemporary life. Recent advances in

miniaturization may make possible vehicles that can carry out important military

missions that heretofore were beyond our reach or could only be attained at great risk or

resource expenditure. These missions will be possible if MAVs can fulfill their potential

to attain certain attributes to include: low cost, low weight, little to no logistical

footprint, mission versatility, range, endurance, stealth, and precision.

A review of the literature in this area indicates that the military potential of this

emerging field remains on the technological push side of the equation with little to no

requirements pull from the user community. Accordingly, concepts of operations

deriving from the war fighting community particularly the United States Air Force

(USAF) are sparse. At a higher level, the potential of micro-air vehicles opens up new

possibilities in the formulation of military strategies that require investigation. This

paper provides an outline of the contemporary technological dimension of MAVs and

contemplates how they might be used to enhance Air Force operations.

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Chapter 1

Introduction

A two-ship of enemy fighters taxies to the end of the runway to conduct

their last checks before take-off. Just as the aircraft rev their engines ahandful of aircraft a bit smaller than model airplanes dive down from an

altitude of 300 feet. Unseen by airfield observers because of their small

size, these innocuous vehicles home in on the fighters engine intakesusing a combination of imaging infrared and acoustical sensors. Darting

into the intakes they quickly cause foreign object damage and engine

shutdown. There will be no glory in aerial combat for these fighterstoday.

A possible wartime scenario in the not too distant future

There are many pressures on todays U.S. military. The variety in the nature of

threats and other challenges expands daily. Potential adversaries get smarter all the time

and their access to modern weaponry appears uninhibited. There is no let up in

operations tempo. The lag between cutting edge technologies and those installed in newly

fielded military systems appears to be worsening. Efforts to contain costs meet with

limited success at best.

That the U.S. continues to exercise its unqualified leadership in military matters

around the globe in the face of such pressures is a tribute to its leaders vision as well as

the hard work and ingenuity of its people. The soundness of such leadership and its

underpinnings are attested to by the preeminence of our nations air forces which more

and more are being pushed to the front lines of conflict. They have become the

weapons of choice for handling difficult duties throughout the world. Without taking

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anything away from the military people who make this preeminence a daily reality, it is

no less founded on the superior war fighting capabilities inherent in our systems and

technology. These advanced technologies provide an asymmetric advantage to U.S.

forces at least to the extent the U.S. acquires them first and forges their incorporation into

concepts of operation.

One area of technological advancement that holds promise to help the U.S. maintain

its military leadership is the emerging field of micro-air vehicles (MAV). Technological

progress in a number of areas to include aerodynamics, microelectronics, sensors, micro-

electromechanical systems (MEMS), micro-manufacturing, and more, is ushering in the

possibility for the affordable development and acquisition of this new class of military

systems. MAVs are a subset of uninhabited air vehicles (UAV) that are roughly two

orders of magnitude smaller than the manned systems that permeate our contemporary

life. Recent advances in miniaturization may make possible vehicles that can carry out

important military missions that heretofore were beyond our reach or could only be

attained at great risk or resource expenditure. These missions should be possible if

MAVs fulfill their potential to attain certain characteristic attributes to include: low cost,

low weight, little to no logistical footprint, mission versatility, range, endurance,

stealth, and precision. Micro-air vehicles may represent a pioneering advancement

providing the U.S. a new asymmetric advantage.

A review of the literature in this area indicates that the military potential of this

emerging field remains on the technological push side of the equation with little to no

requirements pull from the user community. Accordingly, concepts of operations

deriving from the war fighting community particularly the United States Air Force

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Chapter 2

Why Micro-Air Vehicles?

What Makes Micro-Air Vehicles Unique?

As stated above, MAVs are a subset of UAVs characterized by their relatively small

size. This small size implies a number of potentialities to include the following:

MAVs may be more amenable to a faster, better, cheaper approach to theirdevelopment, procurement, and fielding

It should be possible to design MAVs to have a small (even negligible) logisticsfootprint

MAVs may afford a commodity approach to mission accomplishment either byenabling a variety of payloads to be manufactured for a single airframe or byproving flexible enough to permit payload variation in the field

MAVs may prove a cost-effective augmentation to existing, overtaxed systems MAVs may bring mission capabilities to smaller units that heretofore were not

large enough to justify possession and operation of traditional systems providingsuch capabilities

MAVs may afford the U.S. asymmetric avenues in the conduct of warfareWhile the diminutive nature of micro-air vehicles makes possible their advantageous

employment in a variety of military settings, it also comes with constraints that must be

acknowledged and taken into account for proper tactical use. Likewise, the fact that

MAVs can be found within a spectrum of UAV capabilities provides an onus to avoid

redundancy and to optimally focus use on applications that leverage their unique

characteristics.

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Table 1 below provides a listing of the spectrum of UAVs and the relative place of

micro-air vehicles within it.

Table 1. UAV Classifications, Characteristics, & ExamplesCategories Abbreviation Datalink Range

(km)Endurance

(hours)Maximum Flight Altitude (m) Launch Method Recovery Method

Nano unknown

Tactical UAVs

unknown unknown unknownunknown

Example Missions: speculativeExample Systems: none known

Meso unknown unknown unknown VTOL BellyExpendable

Example Missions: wide-area sensing (in swarms), planetary explorationExample Systems: Mesicopter

Micro < 10 1 250 H/HL/VTOL Belly, skidsExpendable

Example Missions: RSTA, comms relay, scouting, NBC sampling, EWExample Systems: MicroStar, Hyperav+, Black Widow, Microbat

Mini Mini < 10 < 2 250 HL/L/VTOL/Wheels

Belly, skidsWheels Parachute

Example Missions: film and broadcast industries, agriculture, pollution measurementsExample Systems: Aerocam, RPH2+, R50+, Rmax+, SurveyCopter

Close Range CR 10-30 2-4 3,000 HL/L/VTOL/

Wheels

Belly, skids

Wheels ParachuteExample Missions: Recon, EW, artillery correction, mine detection, search & rescueExample Systems: APID+, Camcopter+, Cypher, Dragon, Javelin, Luna, Mini Tucan, Mi-Tex Backpack,

Observer, Pointer, Vigilant, Vigiplane

Short Range SR 30-70 3-6 3,000 L/VTOL/RATO

Belly-skidsParachutePara/airbag

Example Missions: RSTA, BDA, EW, NBC sampling, mine detectionExample Systems: Crecerelle, Dragon, Eyeview, Fox, Heliot+, Mirach 26, Phantom, Phoenix, SoOJKY,

Sperwer, Vulture

Medium Range MR 70-200 1 3,000-5,000 L/VTOL/Wheels/RATO

SkidsWheelsPara/airbag

Example Missions: RSTA, BDA, artillery correction, EW, NBC sampling, mine detection, comms relayExample Systems: Brevel, CL327+, Eagle Eye+, Mucke, Outrider, Pioneer, Prowler, Ranger, Searcher, Seeker,

Sentry, Shadow 200, Skyeye, Sniper

Low AltitudeDeep Penetration

LADP > 250 1 0.12-9,000 RATO Para/airbag

Example Missions: ReconExample Systems: CL89, CL289, Mirach 100, Mirach 150

Long Range LR > 500 6-13 5,000 Wheels/RATO

Wheels

Example Missions: RSTA, BDA, comms relayExample Systems: Hunter

Endurance EN > 500 12-24 5,000-8,000 Wheels/Launcher

WheelsPara/airbag

Example Missions: RSTA, BDA, comms relay, EW, NBC samplingExample Systems: Aerosonde, Hermes 450, Prowler II, Searcher II, Shadow 600, Super Vulture

Medium AltitudeLong Endurance

MALE > 500

Strategic UAVs

24-48 5,000-8,000 RLG RLG

Example Missions: RSTA, BDA, comms relay, EW weapons deliveryExample Systems: Altus, Hermes 1500, Heron, I. Gnat, Perseus, Predator, Theseus

High AltitudeLong Endurance

HALE > 1,000 12-40 15,000-20,000 RLG RLG

Example Missions: RSTA, BDA, comms relay, EW, boost phase intercept launch vehicleExample Systems: GlobalHawk, Raptor, Condor

Lethal 300

Special Purpose UAVs

4 3,000-4,000 Launcher/RATO/Air-Launch

Expendable

Example Missions: Anti-tank/vehicle, anti-radar, anti-infrastructure, anti-ship, anti-aircraftExample Systems: Harpy, K100, Lark, Marula, Polyphem, Taifun, Sea Ferret, MALI

Decoys 0-500


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What Is the Basis for an Air Force Interest in MAVs?

From a military point of view, micro-air vehicles are attractive for a number of

reasons. The leading motive would appear to be the promise they hold to support

activities in the realm of information operations, particularly support for intelligence,

surveillance, and reconnaissance (ISR) before, during, and after events of interest. These

functions will be executed through carriage and operation of miniaturized sensors. As

conveyed in Joint Vision 2020, the Joint Chiefs of Staff manifesto for the future of

Americas military:

The evolution of information technology will increasingly permit us to integrate thetraditional forms of information operations with sophisticated all-source intelligence,surveillance, and reconnaissance in a fully synchronized information campaign. . . .Information superiority is fundamental to the transformation of the operationalcapabilities of the joint force. The joint force of 2020 will use superior information andknowledge to achieve decision superiority, to support advanced command and controlcapabilities, and to reach the full potential of dominant maneuver, precision engagement,full dimensional protection, and focused logistics.2

What this means, among other things, are greater battlespace awareness and reduced

decision cycle times. To the extent MAVs contribute to these goals, as favorably

compared to other alternatives, their use in military contexts will appear inviting.

The USAF is fully on board with this Joint Staff vision. In Americas Air Force

Vision 2020, the Air Force leadership states,

[W]ell provide the ability to find, fix, assess, track, target and engage anything ofmilitary significance, anywhere. . . . Information superiority will be a vital enabler of thatcapability. . . .

Capitalizing more fully on a set of revolutionary technologies like stealth, advancedairborne and spaceborne sensors and highly precise all-weather munitions well operatewith greater effectiveness . . . With advanced sensors and a range of precise weapons,from large to very small, well be able to strike effectively wherever and whenevernecessary with minimum collateral damage.3 [emphasis added]

2 Joint Chiefs of Staff,Joint Vision 2020 (Washington, D.C.: Government Printing Office, June 2000), 9-10, available from http://www.dtic.mil/jv2020.3 General Michael E. Ryan and F. Whitten Peters,Americas Air Force Vision 2020, no date, 12; on-line,Internet, 8 December 2000, available from http://www.af.mil/vision/.

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other five capabilities, one has some relevance to MAVs, that being Projection of

Lethal and Sublethal Power. A system proposed in this vein is a robotic micro

munition designed to attack deeply buried hard targets. The study also identifies key

technologies for development that will support its vision and worth highlighting are

micro-sensors having novel readout methods and low probability of intercept as well

as [m]icro-electromechanical systems for sensing and manipulating.4

One other official document which speaks to MAV-like systems resulted from an

effort directed by the Chief of Staff of the Air Force known as Air Force 2025. This

study outlined several alternate futures or environments to facilitate its strategic

planning methodology and defined them as an array of [possible] future worlds in which

the U.S. must be able to survive and prosper. Within this context the study team

identified 10 top systems among 40 envisioned, including a concept known as attack

microbots. This concept is described as

. . . a class of highly miniaturized (one millimeter scale) electromechanical systemscapable of being deployed en masse and performing individual or collective target attack.

Various deployment approaches are possible, including dispersal as an aerosol,transportation by a larger platform, and full flying and crawling autonomy. Attack isaccomplished by a variety of robotic effectors, electromagnetic measures, or energeticmaterials. Some sensor microbot capabilities are required for target acquisition andanalysis. Microbots could provide unobtrusive, pervasive intervention into adversaryenvironments and systems. The extremely small size provides high penetrationcapabilities and natural stealth.

In assigning this concept a role in future interdiction missions the study said, Penetrating

sensors and designators, coupled with micro-technology, will permit weapons to have the

processing power required to touch targets in the right spot.5

4 Air Force Scientific Advisory Board,New World Vistas Air and Space Power for the 21st CenturySummary Volume, 1995, n.p.; on-line, Internet, 4 December 2000, available from http://www.sab.hq.af.mil/Archives/1995/NWV/vistas.htm.5Air Force 2025, August 1996, n.p.; on-line, Internet, 18 December 2000, available fromhttp://www.au.af.mil/au/2025/index2.htm.

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While not one of the top 10, the Air Force 2025 study also identified a concept

known as miniature unattended ground sensors (MUGS) to support the intelligence,

surveillance, and reconnaissance function. These devices would be air-dropped as a

swarm in the vicinity of a supply chokepoint and become a remote sentry reporting on

enemy activity. In this capacity miniature unattended ground sensors would help guide

munitions as well as report on munitions effects. Predicting just how far the technology

might advance, the study asserted that a MUGS of 2025 with a complete suite of

communications and power capabilities, camouflage, and either motive or adhesive

systems would be one centimeter square by one millimeter thick. It further stated that

miniature unattended ground sensors would be ideal for detecting weapons of mass

destruction and operating in urban environments.6

To enable these and other concepts to become a reality, the Air Force 2025 study

identified six high leverage technologies which stood out because they are important

to a large number of high-value system concepts. Among these were micro-

mechanical devices which has already been alluded to above as MEMS.7 Such devices

are sized on the order of hundreds of microns and represent fully functional mechanical

machines sometimes combined with electronic devices and manufactured through

lithography or similar techniques used in computer chip production. Given the centrality

of micro-electromechanical systems to MAVs and other micro-robotic systems, their

development should be viewed as a critical path item.

6 Ibid.7 Ibid. The other five high leverage technologies were data fusion, power systems, advanced materials,high energy propellants, and high performance computing.

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Another organization expressing interest in micro systems for Air Force application

is RAND. While not an official source of Air Force opinion, RAND has nonetheless

proven itself a significant influence over Air Force thinking in the realms of technology

and policy. In Technology Trends in Air Warfare senior RAND analyst, Benjamin

Lambeth, envisions [m]icrosensor-directed micro-explosive bombs . . . able to kill

moving targets with just grams of explosive. Additionally, he sees a time when

[g]round weather sensors can be delivered by small UAVs aboard larger UAVs.8

Another RAND study,Military Applications of Microelectromechanical Systems, posited

a number of concepts to demonstrate how MEMS could have military utility and while

none of them was specifically a micro-air vehicle type system in itself, each could be

married up to a MAV to enable a useful mission. These concepts included the following:

Chemical sensor for the soldier Identification friend or foe Active surfaces Distributed sensor net Micro-robotic electronic disabling system

The first concept, if carried aloft by a MAV, would allow remote sensing of noxious

battlefield agents such as nuclear, biological, and chemical products. The second could

be delivered by MAVs to facilitate targeting of enemy resources and avoidance of

fratricide. The third could be a means at the subsystem level to enhance MAV

aerodynamic performance. The fourth MEMS concept would allow the commander to

blanket an area [with micro-sensors] with a single shot, or to use micro-sized UAVs for

seeding.

8 Benjamin S. Lambeth, Technology Trends in Air Warfare, RAND Reprint RP-561 (Santa Monica, CA:RAND, 1996), 139-141.

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The micro-robotic electronic disabling system concept involves target attack and

disabling via infiltration of the targets electronics. It would be dispensed in the general

neighborhood of the target via carrier vehicle such as an UAV. The micro-robotic

electronic disabling system would be contained within small canisters that would fly or

glide (via aerobot, parafoil, etc.) to within a short distance of their target(s). From

there they would then move on their own to infiltrate and deliver the kill mechanism.

Targets vulnerable to micro-robotic electronic disabling systems would include: power

plants/relay stations, transportation grid nodes, airports, seaports, switching yards, major

freeway intersections, television/radio stations, telephone exchanges, computer/research

centers, and electronics at key industrial sites.9

As can be seen from this limited set of sources, the Air Force certainly has reason to

be interested in micro-air vehicles. They hold potential to provide military worth by

supporting global awareness and power projection operations. Despite such potential,

there is only one dedicated research and development (R&D) program under Air Force

sponsorship known to the author that is looking at how MAVs could be optimized for Air

Force missions.10 Instead, interest appears to be greater in other military circles.

Who Else Is Interested in MAVs?

The Army, Navy, and Marines currently appear to be showing much greater interest

in micro-air vehicles than the USAF. Interest in these aircraft has also appeared from

civilian quarters as well.

9 Keith W. Brendley and Randall Steeb,Military Applications of Microelectromechanical Systems, RANDReport MR-175-OSD/AF/A (Santa Monica, CA: RAND, 1993), 16-30.10 This effort, sponsored by the Air Force Office of Scientific Research at Arizona State University, islooking at low Reynolds Number aerodynamics and unsteady gust effects on MAVs. The grant willconclude in 2001.

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Military

Currently, the bulk of U.S. R&D sponsored by the military in micro-air vehicle

technologies comes from the Defense Advanced Research Projects Agency (DARPA).

DARPA is now in the third year of a $35 million four-year program in which MAVs and

supporting technologies are being developed and demonstrated.11 This program can

trace its roots back to two workshops hosted by RAND in the early 1990s in which

several technologies were identified warrant[ing] greater U.S. defense R&D

investment. Among these promising program areas was development of miniature

(e.g., fly-size) flying and/or crawling systems capable of performing a wide variety of

battlefield sensor missions.12 Later, in the mid-1990s, the Massachusetts Institute of

Technology (MIT) Lincoln Laboratory did some technical analyses which pointed to the

feasibility of MAVs. Not stopping there, they devised a conceptual design and presented

it to then Vice Chairman of the Joint Chiefs of Staff, Admiral William Owens. Upon

being asked if he saw potential utility in such a machine, the Admiral was impressed

enough to encourage the Lincoln Laboratory researchers to continue their work in the

field and to challenge his brethren in the naval R&D community to do the same.13

According to DARPA micro-air vehicle program representatives,

[t]he shift toward a more diverse array of military operations, often involving small teamsof individual soldiers operating in non-traditional environments (e.g., urban centers), isalready evident in the post-cold war experience. . . .

In contrast to higher-level reconnaissance assets like satellites and high altitude UAVs,MAVs will be operated by and for the individual soldier in the field as a platoon level

asset, providing local reconnaissance or other sensor information on-demand, where andwhen it is needed.

11 Michael A. Dornheim, Tiny Drones May Be Soldiers New Tool,Aviation Week & Space Technology148, no. 23 (8 June 1998): 42-43.12 Richard O. Hundley and E. C. Gritton,Future Technology-Driven Revolutions in Military Operations:Results of a Workshop, RAND Documented Briefing DB-110-ARPA (Santa Monica, CA: RAND, 1994),11.13 Richard J. Foch, Naval Research Laboratory, interviewed telephonically by author, 15 November 2000.

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the radar signal. What the jammer lacks in power, would be compensated for by

reduction in distance to the victim receiver.18

Civilian

It is difficult to gauge how much R&D is being conducted by commercial firms

insofar as almost all the literature dealing with the subject relates to military sponsored

work. Still, even for efforts paid for by the military, the developers are quick to point out

civilian applications for MAV systems. Dr. Samuel Blankenship at the Georgia Tech

Research Institute (GTRI) foresees use of MAVs by police and fire officials, scientists,

and farmers. Tasks might include killing harmful insects, measuring smokestack

emissions, monitoring concentrations of chemicals in agricultural or industrial spills,

surveying wildlife, and providing recreation as toys.19 Still other possibilities mentioned

include: traffic monitoring, border surveillance, forestry, power-line inspections, real-

estate photography,20 hostage crisis monitoring,21 search and rescue (such as

maneuvering through damaged buildings looking for survivors after a disaster), locating

illegal drugs or weapons,22 surveillance of criminal activities,23 replacing weather

18 S. Carroll, US Navy, DARPA Develop IMINT/EW Payloads for Mini-UAVs,Journal of ElectronicDefense 21, no. 9 (September 1998): 30-32.19 Amy Stone, Flying into the Future,Research Horizons Georgia Institute of Technology, 24 February1998, n.p.; on-line, Internet, 23 October 2000, available from http://www.gtri.edu/rh-spr97/microfly.htm. 20 McMichael and Francis.21 Mark Dwortzan, Reporter: Its a Fly! Its a Bug! Its a Microplane! Technology Review, October 1997,n.p.; on-line, Internet, 23 October 2000, available from http://www.techreview.com/articles/oct97/reporter.html.22 Douglas Page, Micro Air Vehicles: Learning from the Birds and the Bees,High Technology CareersMagazine, 1998, n.p.; on-line, Internet, 23 October 2000, available from http://www.hightechcareers.com/doc198e/mav198e.html. 23 United Kingdom Defence Forum, TS6. Micro Air Vehicles, March 1999, n.p.; on-line, Internet, 23October 2000, available from http://www.ukdf.org.uk/ts6.html.

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balloons, serving as temporary antennas,24 crowd monitoring and control,25 home

security, and the entertainment industry.26

It appears that unlike other trends in defense related R&D, the tide has not yet turned

for micro-air vehicle technologies wherein the military can depend on commercial

interests to lead the way in development as has occurred in the microelectronics industry.

Instead, the military will have to continue to provide the seed resources and leadership

to promote advances in this area. Still, as shall be seen, enough progress may have been

made over the past decade that more of the R&D burden can be shared between these

communities in the future.

24 Jerome Greer Chandler, Micro Planes,Popular Science 252, no. 1 (January 1998): 54.25 David Pescovitz, Tiny Spies in the Sky, undated, n.p.; on-line, Internet, 23 October 2000, available from http://www.discovery.com/stories/technology/microplanes/. 26 Denis Susac, Micro-Air Robots, 20 July 1999, n.p.; on-line, Internet, 23 October 2000, available fromhttp://www.ai.about.com/computer/ai/library/weekly/aa072099.htm.

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An approximate vehicle weight of 50 grams (~ 1.75 ounces)29 A useful payload weight of about 20 grams (~ 0.70 ounces) An endurance of 20-60 minutes An operating range out to 10 kilometers (~ 6 miles) A cruising speed of between 10 and 20 meters per second (m/s, ~ 22-45 miles per

hour)30

A unit production cost of $5,000 (near term) down to $1,000 (far term)31The dimensional limit chosen by DARPA was no accident as both physics and

technology considerations come into play.32 As shall be discussed below, aerodynamic

characteristics begin to diverge from the norm at this size and miniaturization of

components becomes hard pressed as well. Furthermore, DARPA desired to push the

technology involved, on the grounds that this value [15 centimeters] is half a foot, and a

foot looked too easy.33

It is self evident that a micro-air vehicle is a system composed of constituent

subsystems. It is at this subsystem level that many of the technology challenges present

themselves. That said, it is very important to realize that unlike many other, larger

systems, MAVs present a rather difficult systems engineering challenge. This is because

for MAVs to be successful, they will require high degrees of system integration with

unprecedented levels of multifunctionality, component integration, payload integration,

and minimization of interfaces among functional elements.34 Additionally, extremely

29 There appears to be some variation in this parameter given the different goals various researchers appearto be pursuing. A number of sources state weight limits roughly twice (100 grams or 4 ounces) or morethan what DARPA has set out as the goal for their program. See Bruce D. Nordwall, Micro Air VehiclesHold Great Promise, Challenges,Aviation Week & Space Technology 146, no. 15 (14 April 1997): 67;Steven Ashley, Palm-size Spy Plane,Mechanical Engineering, February 1998, n.p.; on-line, Internet, 16November 2000, available at http://www.memagazine.org/backissues/february98/features/palmsize/palmsize.html; S. Carroll, 30; Pescovitz; and UK Defence Forum.30 McMichael and Francis.31 Keeter.32 Mark Hewish, Rucksack Recce Takes Wing,Janess International Defense Review 30 (February1997): 63.33 Hewish, A Bird in the Hand, 22.34 Ashley, Palm-size Spy Plane.

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constrained weight and volume limits and high surface-to-volume ratios mean the

traditional practice of stuffing more into the airframe shell will probably not suffice.

Instead each of the MAVs components must perform as many functions as possible.35

An example of this would be antennas embedded in the surface skin of the MAV

providing signal reception as well as bearing structural loads. Beyond the surface,

weight, and volumetric concerns, close coupled, dynamic electromagnetic and thermal

interactions will be even greater issues than they are for larger systems.36

Despite the high level of integration and multi-functionality required, it is still useful

to break out each major aircraft subsystem to discuss the progress made by and issues

facing micro-air vehicle designers. Table 2 below provides an example breakout that

reflects mid-1990s technological limitations in which propulsion weight (and most likely

energy storage/conversion as well) dominates.

Table 2. Baseline MAV Weight Distribution

Component Weight in grams (ounces)

Airframe 6 (0.2)Propulsion 36 (1.7)

Flight Control 2 (0.1)

Communications 3 (0.1)

Visible Sensor 2 (0.1)

Total Weight 49 (1.7)

Source: Adapted from W. R. Davis, et al., Micro Air Vehicles forOptical Surveillance, The Lincoln Laboratory Journal9 (1996): 197-214.

While this component or subsystem listing is a somewhat representative one, the

discussion here will use a slightly different breakdown. To this end the following areas

will be treated individually: aerodynamics, propulsion, energy generation and storage,

guidance and navigation, communications, and finally payloads.

35 Justin Mullins, Palmtop Planes,New Scientist154, no. 2076 (5 April 1997): 41.36 Ashley, Palm-size Spy Plane.

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separates easily leading to stall which is a major loss of lift and increase in drag. More

generally, lift performance is rather poor in this regime and skin friction drag is elevated

due to relatively large viscous forces. Thus, while MAVs are likely to see lift-to-drag

ratios of about 5 to 10 whether the system uses a fixed wing with propeller, rotor, or

flapping wing design,39 higher Reynolds Number flight vehicles will possess lift-to-drag

ratio values on the order of 3 to 4 times higher.40 As one observer put it, flying at these

conditions would be akin to swimming in honey if translated to the scales to which

humans are accustomed.41

At low Reynolds Numbers, the unsteadiness in the freestream velocity becomes

more significant which means phenomena such as gusts can effect a small vehicle

considerably.42 Also, a characteristic known as hysteresis becomes a problem as well.

Hysteresis is a performance anomaly in which the lift and drag developed by an airfoil

(wing shape) are quite different at a given angle of attack depending on whether that

incidence to the flow was approached from lower or higher values.

Flight Controls

Given these unusual flow phenomena, achieving efficient and stabilized flight is a

significant challenge. The answer may lie in the pursuit of passive and/or active control

strategies using micro-electromechanical system type devices to improve aerodynamic

performance and control. As an example, it may be possible to create and install tiny

sensors and actuators to dynamically adjust the camber (i.e., curvature) and shape (i.e.,

39 G. R. Spedding and P. B. S. Lissaman, Abstract for Technical Aspects of Microscale Flight Systems,n.p.; on-line, Internet, 23 October 2000, available from http://ae-www.usc.edu/rsg/bfd/Lund.html. 40 McMichael and Francis.41 Mullins, 39.42 Wei Shyy, Mats Berg, and Daniel Ljungqvist, Flapping and Flexible Wings for Biological and MicroAir Vehicles,Progress in Aerospace Sciences 35 (1999): 496.

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profile) of the wing depending on the instantaneous conditions.43 These miniature

actuators could also be used to move control surfaces like rudders, ailerons, and flaps.

Flow character over the wing could be controlled by sensor arrays that detect the shear

stresses44 or fluid vortices45 at the wing surface coupled with flexible membranes or

micro-flaps to affect the flow as desired. Flow separation could also be mitigated

employing such exotic approaches as air suction/injection along the wing surface (which

might require micro-valves and micro-pumps), wall heat transfer, or electromagnetic

body force.46 Another proposed approach, called circulation control, 47 is to take

advantage of what is known as the Coanda effect. In this technique engine thrust

48

or

exhausted air49 is directed across a wing surface or out the trailing edge so as to help the

flow stay attached and generate additional lift. Blown air could also be used for

providing flight control (stabilization and maneuvering) potentially obviating the need for

moving control surfaces.50

Stabilization will require optimized design and integration of whatever sense and

control schemes are employed. On the sensor side, angular rate, pressure, or acceleration

transducers could be used to help provide stability augmentation. Micro-motors,

piezoelectric devices, electrostatic or electromagnetic mechanisms,51 magnetoelastic

43 Ibid., 486.44 Bruce Carroll, MEMS for Micro Air Vehicles,Project Summaries, n.p.; on-line, Internet, 24 August2000, available from http://www.darpa.mil/MTO/MEMS/Projects/individual_66.html. 45 Hank Hogan, Invasion of the Micromachines,New Scientist150, no. 2036 (29 June 1996): 31.46 Gad-el-Hak, Mohamed, Micro-Air-Vehicles: How Can MEMS Help?Proceedings of theConference on Fixed, Flapping and Rotary Vehicles at Very Low Reynolds Numbers, 5-7 June 2000,University of Notre Dame, ed. Thomas J. Mueller, 210-211.47 Chandler, 55.48 Mullins, 39.49 Page, Micro Air Vehicles: Learning from the Birds and the Bees.50 Mullins, 39.51 Ashley, Palm-size Spy Plane.

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uncharted territory.69 Still, this technology could conceivably be available within a

year or two.70 The Massachusetts Institute of Technology Gas Turbine Lab is working on

a silicon carbide engine that weighs 1 gram (0.04 ounces) is only 1 centimeter (0.4

inches) in diameter and 0.3 centimeters (0.12 inches) thick, yet produces 10 to 20 watts of

power. A working combustor has been built, but the compressor, generator, and bearings

have yet to be perfected at micro scales.71 The program goal is to produce 13 grams

(0.03 pounds) of thrust.72 Eventually, thrustto-weight ratios approaching 100:1

(compared with 10:1 for the best modern fighter aircraft engines) and fuel consumption

rates of 10 grams per hour should be possible using hydrogen fuel. MIT design

calculations indicate that for the device to have sufficient power density, the combustor

exit temperature needs to be 1,000 to 1,500 degrees Centigrade and rotor peripheral

speeds 300 to 600 meters per second (~ 1000 to 2000 feet per second).

MIT is not the only one working in this area as the United Kingdoms (UK) Defence

Evaluation and Research Agency (DERA) has successfully produced and demonstrated

their own variant of a microjet. The device is 1.3 centimeters (0.5 inches) long by 0.5

centimeters (0.2 inches) diameter and weighs in at less than 2 grams (0.07 ounces). It

uses a hydrogen peroxide-kerosene fuel mixture and has achieved 6.4 grams (0.01

pounds) of thrust and flight duration times of up to an hour. Starting and stopping the

engine has proven simple and reliable.73

69 Michael A. Dornheim, Turbojet on a Chip to Run in 2000,Aviation Week & Space Technology 151,no. 2 (12 July 1999): 50-52.70 Steven Ashley, Turbines on a Dime,Mechanical Engineering, October 1997, n.p.; on-line, Internet, 16November 2000, available at http://www.memagazine.org/backissues/october97/features/turbdime/turbdime.html71 Chandler, 58.72 Dornheim, Turbojet on a Chip, 50.73 A New Thrust in DERA Micro Air Vehicle Development, 24 July 2000, n.p.: on-line, Internet, 14 December 2000, available from http://defence-data.com/f2000/pagefa1006.htm.

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Electric Motors

When paired with propellers on fixed wing designs or rotor blades on helicopters,

electric motors are another propulsive option for micro-air vehicles. They are quiet,

reliable and dont produce much vibration, but suffer the disadvantage of low power to

weight ratio when coupled with batteries or other power-generation sources.74 According

to the NRL, small new motors using a brushless neodymium-iron-boron magnet design

can achieve 90 percent efficiencies. A lightweight system based on a high-efficiency

electric motor and top of the line lithium batteries could run for 20 to 30 minutes. In its

sponsored research, the NRL is shooting for a pencil-shaped motor weighing nor more

than 6 grams (0.2 ounces) (including the controller and any reduction gearing) with a

desired output power of 2 watts and a system efficiency of 80 percent.75

Reciprocating Chemical Muscle

Georgia Tech is pursuing a flapping wing design they have dubbed a microflyer,

but which others using similar approaches call an entomopter or ornithopter in

reference to its insect-like or bird-like characteristics. This micro-air vehicle variant

employs a reciprocating chemical muscle which uses a monopropellent fuel to generate

an up and down or back and forth motion such as the beating of wings or scurrying of

feet. Like the micro-turbine, the reciprocating chemical muscle can also be used to

generate electricity that could be used to power sensors or other on-board systems.

Georgia Tech researchers believe a self-consuming system is possible in which the

microflyer would consume itself to generate energy as it flies. Alternately the

reciprocating chemical muscle concept is even amenable to conversion of biomass into

74 UK Defence Forum, TS6. Micro Air Vehicles.

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usable fuel reactions. Thus, future microflyers may be able to gather fuel from the

environment to continue their operations.76 A 50-gram (1.8-ounce) microflyer possessing

a reciprocating chemical muscle with 100% efficiency would need just over a watt of

power. One cubic centimeter of fuel would suffice for 3 minutes of flight.77

Energy Generation and Storage

As was observed in the last section, internal combustion engines and micro-turbines

can be used to convert liquid fuel into thrust and electricity for use by other subsystems.

That said, whether the energy comes as a by-product of the propulsion process or from a

separate dedicated on-board source, the relatively large amount of power that must be

supplied to the propulsion system means less is available for other subsystems.

Therefore, challenges for micro-air vehicle design are to generate and/or store sufficient

energy within the tiny craft (i.e., attain high power density) and to adhere to strict power

budget allocations.

As far as energy source options, the two leading contenders appear to be lithium

batteries and fuel cells with the former more likely to find near-term application.

Beamed microwave energy is also being investigated. Compared to a rechargeable Nicad

battery of the same weight and at a high discharge rate, a lithium battery delivers several

times the energy.78 Nevertheless, lithium batteries need to advance in terms of energy

density from 200-500 joules per gram to the range of 700-900 joules per gram. Likewise,

power drain rates need to increase from the present level of 0.06-0.2 watts per gram to

75 Hewish, A Bird in the Hand, 27.76 Stone.77 Hewish, A Bird in the Hand, 26.78 Mullins, 41.

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about 0.5 watts per gram to enable sustained climbing flight.79 One recent advance of

note is a new lithium battery that can be recharged by sunlight and which comes as a thin,

flexible sheet. This configuration may allow the battery to double as the surface of a

MAV.80 One estimate is that this thin-film lithium battery technology could provide

enough power to allow one gram to hover almost 5 hours or fly 10 kilometers and still

retain 80 percent of its energy.81

While fuel cell technology is less mature, it should provide 2-4 times the energy

density of a lithium battery. Fuel cells promise clean, quiet operation with instant start-

up and cold-weather operation. They are also non-toxic and have virtually unlimited

shelf life with no required periodic maintenance. DARPA is sponsoring development of

a small, lightweight, one-time use, non-regenerative solid-oxide fuel cell roughly 1

centimeter tall and weighing just 25 grams. Such a fuel cell would run to completion

once the reaction is started, last about 1 to 2 hours, and provide all the power a MAV

should need. All in all, this technology could be ready in the next few years.82

A last option is to dispense with on-board carriage of stored or generated energy and

to beam microwave power to the micro-air vehicle from the ground. Obviously, the

drawback to such a scheme is that it depends on the ground-based microwave source that

consists of a variety of equipment from transmission dishes to tracking and aiming

devices to transportation gear.83 Researchers at the Naval Postgraduate School are

working on ways to beam power to a MAV and included in their efforts is a multi-

directional antennae able to send energy no matter what direction the MAV is. They

79 Hewish, Rucksack Recce Takes Wing, 63.80 Mullins, 41.81 Page, Micro Air Vehicles: Learning from the Birds and the Bees.82 Ashley, Palm-size Spy Plane.

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will be attractive for this application because of their high data bandwidths and their

wavelengths of only a few centimeters which translates into small antenna size. As it

stands now transmission ranges are on the order of a couple kilometers but this should

improve in time such that 10 kilometers (~ 5.4 nautical miles) will soon be possible. 103

As an example of progress in this area, the MicroStar program sponsored by DARPA is

developing a digital datalink that will provide a range of 4-5 kilometers (~ 2.5 nautical

miles) while supporting a 1 megabit per second transmission rate and using only about

200 milliwatts of power.104

MAV Payloads

Like other subsystems, micro-air vehicle payloads will be constrained by weight,

power, and integration limitations. However, the number of useful military functions a

MAV could perform is limited only by the ingenuity of designers and the pace of

technological improvement. Such promise is magnified by the inherent flexibility of the

MAV concept itself. For instance, it should be possible to achieve savings on the

production line by maximizing commodity design and manufacturing approaches. In

those cases where the need for subsystem integration is not too great, MAVs could be

built to allow swap out of some payloads for others105 in the field. While the number and

variety of possible payloads is numerous, this section will focus on what has been

described beyond the stage of a simple concept. Other proposed payloads will be

mentioned but not elaborated upon.

103 Hewish, Rucksack Recce Takes Wing, 63.104 Hewish, A Bird in the Hand, 25.105 Blyenburgh, 31-33.

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Imaging Sensors

The intelligence, surveillance, and reconnaissance function is probably the leading

driver behind the first generation of micro-air vehicles because of its military utility and

the maturity of the supporting technologies. Chip-on-Flex technology is being

employed to miniaturize payload electronics packaging significantly.106 Both tiny

charge-coupled device (CCD)-array cameras and infrared sensors can already support

applications for day/night imaging to sufficient quality to meet mission needs today.

Miniaturization has advanced to the point that researchers at Oak Ridge National

Laboratory have created a camera lens smaller than a coat button.107 An off-the-shelf, 1-

inch long 300 x 240 pixel, black and white video camera weighing 2.2 grams (0.08

ounces) and including a converter for standard National Television Systems Committee

output, has flown. A 15-gram color camera with a 2.4 gigahertz downlink transmitter has

also been demonstrated.108

Another program plans a 512 x 512-pixel day/night camera that can be set to take 30

frames per second or freeze frames once per second.109 This capability should prove

particularly useful considering recent experiences in the Balkans with UAV operations.

When Predator UAV imaging was first made available, fighter aircrew were provided

full-motion video in which the total delay between the real-time event and image

presentation was only 1.5 seconds. However, after working with this capability, aircrew

showed a preference for freeze-frame images updated every few seconds. This allowed

them to better orient themselves on the target as they began their attacks and to obtain

106 John G. Roos, Pocket-size Stalker,Armed Forces Journal, October 1998, 90, and Hewish, A Bird inthe Hand, 24.107 Page, Micro Air Vehicles: Learning from the Birds and the Bees.108 Dornheim, Tiny Drones, 47.

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battle damage assessments within a few seconds of their weapons impact on or near the

targets.110 This human factors consideration should allow engineering and operational

cleverness to create significant reductions in imager power requirements through

adjustment of video frame rates.111

Still another example is the Black Widow micro-air vehicle that is reported to have

carried the smallest video camera ever flown on a remotely piloted aircraft. 112 The

Black Widow was equipped with a commercial low-resolution, sugar-cube-sized video

camera that weighed two grams. The MAVs builders were able to greatly reduce the

cameras size and weight by integrating the support logic with the cameras lenses in

contrast with traditional digital systems that consist of a charge-coupled device imager

wired to four or five support chips.113

The near future could see a visible-light camera, occupying a volume of 1 cubic

centimeter (0.06 cubic inches) and weighing less than 1 gram (0.04 ounces). Such a

camera has been designed by Lincoln Laboratory and would be based on a silicon charge-

coupled device. It would have an aperture of 2.6 millimeters (0.1 inches), contain 1,000

x 1,000 pixels, and produce an image every 2 seconds114 using as little as 25 milliwatts of

power.115 By providing an angular resolution of 0.7 milliradians with a million pixels,

this camera could produce high-definition television quality images that would enable

viewers to tell the difference between a tank and a truck.116

109 David A. Fulghum, Miniature Air Vehicles Fly Into Armys Future,Aviation Week & SpaceTechnology 149, no. 19 (9 November 1998): 37.110 Doug Richardson, High-tech Eyes for Flying Spies,Armada International, May 1999, 61.111 Dornheim, Tiny Drones, 42.112 Richardson, 54.113 Pescovitz.114 Hewish, A Bird in the Hand, 28.115 McMichael and Francis.116 Chandler, 58. This design has not yet received funding for actual build.

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The Jet Propulsion Laboratory (JPL) at the California Institute of Technology is also

pushing the state of the art in miniature solid-state imaging sensors. JPL has developed

ultra-low-power active pixel sensor technology that rests on the commercially available

complementary metal-oxide-semiconductor device fabrication process. This process

allows many components performing different functions to be integrated on a single chip

thus producing cost savings and making possible reductions in system power

consumption by a factor of anywhere from 100 to 1,000.117

Nuclear, Biological, and Chemical (NBC) Agent Sensors

The common wisdom is that biological and chemical agent detectors will require

substantial development before they can find application on micro-air vehicles. The

anticipation is that gradient biochemical sensors . . . will be able to map the size and

shape of hazardous clouds and provide real time tracking of their location.118 Cited as

proof of the challenges ahead is that airborne chemical sensors now weigh about 5

kilograms (11 pounds), while biological sensors of acceptable military utility and

suitability have yet to be fielded.119 However, the situation may not be so bleak as at first

appears. Sandia has unveiled on-going work developing its Lab on a Chip which

essentially is a miniaturized microchemistry lab that will be capable of collecting,

concentrating, and analyzing chemical and biological agents weighing less than a single

bacterium. According to Sandias managers, the miniature labs should be available

within the next decade.120

Research on chemical and biological sensors is also in work at Georgia Tech. There,

117 Hewish, A Bird in the Hand, 28.118 McMichael and Francis.119 Ashely, Palm-size Spy Plane.120 Roos, 90.

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[t]he prototype chemical and biologic sensors are basically small chips of glass withoptical wave guides fabricated on their surfaces which can trap and manipulate light. Onthe most basic level, the sensor would have two channels: sensing and reference. When alaser beam is passed under the strips, the phase of the light contained in the guides isaltered by the change in refractive index that occurs when the sensing channel interactswith the chemical or biological species it is designed to measure.

The information contained in the light is read after the laser beams passing under thesensing and reference channels are combined to generate a unique interference fringepattern, which moves past a solid-state detector array in proportion to the phase changethat has been caused by the sensing interaction. . . .

[U]p to two dozen channels [can be put] on a sensor chip to determine what [an MAV] isflying through. . . .

Already small (about 1 centimeter by 2 centimeters), the sensors will need to be furtherreduced.121

Moving on to radiation sensors, little has been said in the literature about any

progress in miniaturization that would enable characterization of nuclear environments.

Such environments could come about as the result of the explosion of a nuclear device or

damage done to a nuclear weapons facility. Should it be possible to sufficiently

miniaturize a sensor for such a mission, it will most certainly find its way on to a micro-

air vehicle.122

Targeting, Tagging, and Identify Friend or Foe (IFF)

Use of micro-air vehicles for the functions of targeting, tagging, and identification

friend or foe has been mentioned, but little information appears available about what the

state of technology is in this regard.123 A micro-laser rangefinder and designator, as part

of a more extensive micro drone payload, has been proposed by the U.S. Army Dual

Use Science & Technology program.124 A radio-frequency tag125 would presumably be

similar in technology to a communications payload, but attributes of low probability of

121 Stone.122 Kuska.123 McMichael and Francis.124 Richardson, 54.125 Hewish, A Bird in the Hand, 28.

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intercept (LPI) might be necessary when it is used for strike mission aplications. Since a

radio-frequency tag used in this context is essentially a homing beacon, a LPI capability

would mitigate against discovery and removal before a strike attack is completed. Of

course, this would not be a concern for tags emplaced by MAVs to support logistics

needs. Lastly, a variant of a tag could be used for identify friend or foe purposes to aid in

sorting friendlies from the enemy on a chaotic battlefield. An identify friend or foe

system would essentially be different from a tag in its ability to remain quiet until

responding to an interrogation. This implies a receiver train as well.

Explosives and other Lethal Payloads

Although the diminutive size of micro-air vehicles does not greatly inspire thoughts

of their use as explosives delivery platforms, such a possibility is not foreclosed. 126 The

Air Force Research Laboratory currently sponsors work in lightweight, high energy

explosives technology which could lead to munitions suitable for delivery by MAVs. It

does not necessarily take a lot of explosive energy to severely damage a soft target like

a surface to air missile tracking radar if it is hit in the right place. Some observers have

also proposed MAVs as aerial mine-laying platforms127 which could have lethal

consequences for individual personnel or debilitating effects on light vehicles.

One way a micro-air vehicle could deliver a lethal payload would be to employ

poisons of various kinds. Poisons could take the form of a sting or needle in which a

toxin is injected into the victim128 or a dose introduced into something more widely

distributed like a city water supply. Such payloads would have the advantage of being

126 Lambeth, 139.127Hewish, A Bird in the Hand, 22.

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Sniffing Sensors

Still another set of potential payloads includes microelectronic sniffers. These

payloads could be used to uncover the existence of conventional explosives132 such as

mines,133 nuclear, biological, and chemical weapons, or illegal drugs.134 One proposal

even has sniffers being developed to track individuals by their scent alone.135

However, in this area too, little exists in the literature to describe how such payloads

would work or if it is reasonable to predict that they will be available any time soon for

integration on MAVs.

Acoustic Sensors

While the details on the workings of acoustic sensors for micro-air vehicle

applications are slim, there is evidence of work going on in this area. For example, the

Small Business Innovative Research program within the U.S. Army is sponsoring work to

develop an inexpensive micro-acoustic sensor for UAVs that would detect and identify

ground vehicles and provide their location. Although a bit large by MAV standards, the

sensor would be similar in size and cost to a commercial pager and would possess a range

of several kilometers.136 Work sponsored by DARPA developing the Microbat MAV

is also reported to include an option to fly a test vehicle fitted with a microphone array

for acoustic homing on sounds.137

132 Pescovitz.133 Chandler.134 Page, Micro Air Vehicles: Learning from the Birds and the Bees.135 Mullins, 31.136 Hewish, A Bird in the Hand, 28.137 Dornheim, Tiny Drones, 43.

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Other Payloads

Two other areas where specialized payloads could be placed on micro-air vehicles

include applications supporting combat search and rescue and weather measurement.

One proposal has MAVs being packed into the ejection seat mechanisms of high-

performance aircraft which would deploy as the aircrew parachutes down.138

Alternately, a MAV could be placed in aircrew survival gear for hand launch after

parachute landing. These MAVs could carry signal sources, imaging sensors, or

communications relay packages. However, none of these applications requires

technologies inherently different than that discussed above.

Weather sensor payloads have also been proposed.139 The concept would involve

distributing a number of micro-air vehicles across an area of interest with each MAV

possessing a specialized payload that would measure one or more specific parameters

(e.g., pressure, temperature, winds, humidity, etc.). Weather MAVs could begin their

measurements while airborne and/or after landing when fuel for propulsion was

exhausted then continue reporting until energy for measurement and communications was

no longer available (battery exhaustion or solar cell failure).

Weather payloads appear particularly well-suited for use of miniaturized transducer

and micro-electromechanical system technologies. Indeed, this concept would appear

entirely feasible within the next few years save for limitations to communications range.

One reason for such optimism comes from the strides being made in the Smart Dust

program whose goal is to demonstrate that a complete sensor/communication system

can be integrated into a cubic millimeter package. This work, funded by DARPA, has

138 McMichael and Francis.139 Lambeth, 141.

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demonstrated a cubic inch weather package (temperature, humidity, pressure, light

intensity, and magnetic field sensors) with a laser transmitter that provided one weeks

continuous operation and the ability to report its measurements over a 21 kilometer

(~ 11 nautical mile) distance. While continued work is required to achieve even greater

levels of miniaturization, research into distributed algorithms is also necessary to

achieve sensor fusion, that is, a melding of the all the data collected over an array into a

useful summary. 140

140 Kris Pister, Joe Kahn, and Bernhard Boser, Smart Dust, Autonomous Sensing and Communication in aCubic Millimeter, n.p.; on-line, Internet, 23 October 2000, available from http://robotics.eecs.berkeley.edu/~pister/SmartDust/.

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Chapter 4

Micro-Air Vehicle Support to USAF Functions and

Likely Employment Contexts

In Air Force Doctrine Document 1 (AFDD 1) the functions of Aerospace Power

are listed and described.141 Micro-air vehicles would appear to support many, but not all

of these functions and in the listing below, those holding promise are indicated by an

asterisk (*).

Counterair (including Offensive Counterair* and Defensive Counterair) Counterspace (including Offensive Counterspace and Defensive Counterspace) Counterland (including Interdiction* and Close Air Support*) Countersea Strategic Attack* Counterinformation (including Offensive Counterinformation* and Defensive

Counterinformation) Command and Control* Airlift Air Refueling Spacelift Special Operations Employment* Intelligence* Surveillance* Reconnaissance* Combat Search and Rescue* Navigation & Positioning Weather Services*

Each asterisked item above will be defined and discussed in turn to investigate how

MAVs could play a potential future role in Air Force functions across the spectrum of

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military operations. (The definition of each term presented here is as given in AFDD 1.)

But before doing so, it is necessary to address a number of MAV limitations that could

have significant effects on how well these functions are performed. These limitations

should be kept in mind in any discussion of potential MAV applications.

MAV Operational Limitations

The most obvious limitations to micro-air vehicle capabilities will be in range,

autonomy, precision, endurance, damage potential, and from weather. Ways to mitigate

these limitations will have to be found if MAVs are to achieve their full promise.

Range

Micro-air vehicle range limits will necessitate means to deliver these vehicles to the

vicinity of their desired operating locations. To this end a number of alternatives have

been proposed. MAVs could be dispensed by manned aircraft, larger UAVs (to include

cruise missiles), or munition shapes. This concept is not without precedent as evidenced

by concepts to deliver the new Low Cost Autonomous Attack System by a tactical

munitions dispenser.142 Another alternative is to package MAVs for delivery via artillery

rounds such as 120 millimeter mortar tubes or 155 millimeter howitzers143 in much the

same way that the Armys Tactical Missile System delivers Brilliant Anti-Tank rounds

over large distances.

Micro-air vehicle ranges will also be constrained by inherent transmission and

reception limitations. Small antenna and miniaturized avionics will necessitate MAVs

141 Air Force Doctrine Document (AFDD) 1,Air Force Basic Doctrine, September 1997, 45142 Robert Wall and David A. Fulghum, New Munitions Mandate: More Focused Firepower,AviationWeek & Space Technology 153, no. 13 (25 September 2000): 78.143 Hewish, A Bird in the Hand, 28.

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having to remain close to their launch controllers and/or intended recipients of video or

other data. Enemy jamming could prove difficult to cope with given their power

advantage. One way around this constraint would be to use MAVs in swarms wherein

communication ranges are decreased through use of point-to-point relay. Alternatively, a

mother ship concept could be employed where an airborne relay loiters above a MAV

operating area to serve as a signal booster.

Autonomy

To the extent that micro-air vehicles are autonomous, the greater their ability to carry

out their missions without supporting elements such as human flight controllers.

Additionally, some missions, such as military operations in urban terrain, will only be

accomplished with limited effectiveness unless capabilities such as autonomous obstacle

avoidance can be incorporated.

Precision

Lack of positional precision in micro-air vehicle location will constrain their use in

targeting, strike, intelligence, surveillance, reconnaissance, and combat search and

rescue. For example, target geo-location uncertainties are a strong driver in weapons

selection. Battle damage assessments will be made more difficult should it be unclear

which among several similar-looking targets in close proximity a MAV is imaging.

Rescue crews may have to engage threats that could have been avoided had they received

more accurate data on where downed aircrew are located.

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Endurance

The longer a micro-air vehicle and its payload are capable of operating, the better for

most Air Force functions. Longer operation translates into greater mission flexibility and

less frequent need to replace expended MAVs. It also means fewer systems will have to

be purchased which saves costs. This is why progress in energy generation and storage

capabilities for MAVs is so important.

Damage Potential

Micro-air vehicles are by definition small and any mini-munitions they are capable

of delivering will have more effect the more accurate they are in delivery and the more

energetic the blast. This is obviously an area for system engineering trade-offs, but

advances in precision and munitions technologies will enhance the potential to do

damage. However, for the near- to mid-term, it would be unrealistic to expect MAVs to

ever have anything other than a very localized destructive effect.

Weather

As discussed earlier, micro-air vehicles are sensitive to disturbances in the

atmosphere. Aerodynamic control will be difficult under conditions of moderate to high

winds and precipitation; thus, image stabilization for intelligence, surveillance, and

reconnaissance variants will be a challenge. The upper limit for MAV operations in

winds may be no more than 30 miles per hour. This limitation may be particularly

restrictive in urban settings where buildings are known to facilitate the production of

microbursts.144

144 Fulghum, 38.

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Aerospace Power Functions Applicable to MAVs

Offensive Counterair (OCA)

OCA consists of operations to destroy, neutralize, disrupt, or limit enemy air and missilepower as close to its source as possible and at a time and place of [ones] choosing. OCAoperations include the suppression of enemy air defense targets, such as aircraft andsurface-to-air missiles or local defense systems, and their supporting [command andcontrol].

Micro-air vehicles could support offensive counterair in a number of ways. The

vignette presented at the start of Chapter 1 in which MAVs were used to damage enemy

fighters through foreign object damage is one such way. MAVs could also be used as

target beacons for precision strikes against enemy aircraft as well as surface-to-air missile

and command and control assets. MAVs outfitted with mini-explosives could be used to

damage any of these targets to put them temporarily out of action. MAV stealth might be

a particularly strong asset in helping locate SEAD targets that otherwise would refrain

from emitting for fear of attack from SEAD killer platforms.

Interdiction

Interdiction consists of operations to divert, disrupt, delay, or destroy the enemys surfacemilitary potential before it can be used effectively against friendly forces. . . . Interdictionattacks enemy [command and control] systems, personnel, materiel, logistics, and theirsupporting systems to weaken and disrupt the enemys efforts.

Micro-air vehicles could support interdiction in much the same way as they would

offensive counterair. The nature and size of the target set, is however, more varied and in

some respects more vulnerable.

Close Air Support (CAS)

death by a thousand cuts: micro-air vehicles (mav) in the service of air force missions

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